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In this work, we study the photoproduction of ρ$$ \rho $$ mesons considering the proton and the nucleus as the target. Utilizing the dipole picture and the wave functions obtained via AdS/QCD, we were able to describe the HERA γp$$ \gamma p $$ data and extend the formalism to the nuclear case considering the Glauber–Gribov model. The preliminary results obtained in the nuclear regime are compared to the recent LHC PbPb→ρPbPb$$ PbPb\to \rho PbPb $$ data and suggest the presence of a nuclear effect called shadowing. [ABSTRACT FROM AUTHOR]

Cortical stimulation via electrocorticography (ECoG) may be an effective method for inducing artificial sensation in bi-directional brain-computer interfaces (BD-BCIs). However, strong electrical artifacts caused by electrostimulation may significantly degrade or obscure neural information. A detailed understanding of stimulation artifact propagation through relevant tissues may improve existing artifact suppression techniques or inspire the development of novel artifact mitigation strategies. Our work thus seeks to comprehensively characterize and model the propagation of artifacts in subdural ECoG stimulation. To this end, we collected and analyzed data from eloquent cortex mapping procedures of four subjects with epilepsy who were implanted with subdural ECoG electrodes. From this data, we observed that artifacts exhibited phase-locking and ratcheting characteristics in the time domain across all subjects. In the frequency domain, stimulation caused broadband power increases, as well as power bursts at the fundamental stimulation frequency and its super-harmonics. The spatial distribution of artifacts followed the potential distribution of an electric dipole with a median goodness-of-fit of R 2 = 0.80 across all subjects and stimulation channels. Artifacts as large as ±1,100 μV appeared anywhere from 4.43 to 38.34 mm from the stimulation channel. These temporal, spectral and spatial characteristics can be utilized to improve existing artifact suppression techniques, inspire new strategies for artifact mitigation, and aid in the development of novel cortical stimulation protocols. Taken together, these findings deepen our understanding of cortical electrostimulation and provide critical design specifications for future BD-BCI systems.

Urban power transmission and distribution rely on safe operation of vast network of power cables. Majority cable insulation defects can result in partial discharge (PD), which is therefore a degradation mechanism as well as a good indicator of cable insulation condition. Previously published PD models, however, failed to help quantitatively evaluate the insulation condition, or they fail to help differentiate those in between the conditions which are safe to operate from those which may need urgent testing or inspection. PD mechanisms in power cables are reviewed first in this paper. Then a novel model which is based on F distribution is proposed aiming to classify the PD activities which may be associated with different level of degradation. This is based on previous reports that PD activities manifests differently when the levels of degradation of the defect site(s) progress. After that, the features and effects of the model are presented with a case study, and the model is verified by analyzing the waveform similarities. Finally, the nature of the model is compared with the abc-model and the dipole model, demonstrating that proposed model can uniquely recognize the three stages of PD defect development.

Cortical stimulation via electrocorticography (ECoG) may be an effective method for inducing artificial sensation in bi-directional brain-computer interfaces (BD-BCIs). However, strong electrical artifacts caused by electrostimulation may significantly degrade or obscure neural information. A detailed understanding of stimulation artifact propagation through relevant tissues may improve existing artifact suppression techniques or inspire the development of novel artifact mitigation strategies. Our work thus seeks to comprehensively characterize and model the propagation of artifacts in subdural ECoG stimulation. To this end, we collected and analyzed data from eloquent cortex mapping procedures of four subjects with epilepsy who were implanted with subdural ECoG electrodes. From this data, we observed that artifacts exhibited phase-locking and ratcheting characteristics in the time domain across all subjects. In the frequency domain, stimulation caused broadband power increases, as well as power bursts at the fundamental stimulation frequency and its super-harmonics. The spatial distribution of artifacts followed the potential distribution of an electric dipole with a median goodness-of-fit of R2 = 0.80 across all subjects and stimulation channels. Artifacts as large as ±1,100 μV appeared anywhere from 4.43 to 38.34 mm from the stimulation channel. These temporal, spectral and spatial characteristics can be utilized to improve existing artifact suppression techniques, inspire new strategies for artifact mitigation, and aid in the development of novel cortical stimulation protocols. Taken together, these findings deepen our understanding of cortical electrostimulation and provide critical design specifications for future BD-BCI systems.

[Display omitted] Calculating the magnetic interaction between magnetic particles that are positioned in close proximity to one another is a surprisingly challenging task. Exact solutions for this interaction exist either through numerical expansion of multipolar interactions or through solving Maxwell's equations with a finite element solver. These approaches can take hours for simple configurations of three particles. Meanwhile, across a range of scientific and engineering problems, machine learning approaches have been developed as fast computational platforms for solving complex systems of interest when large data sets are available. In this paper, we bring the touted benefits of recent advances in science-based machine learning algorithms to bear on the problem of modeling the magnetic interaction between three particles. We investigate this approach using diverse machine learning systems including physics informed neural networks. We find that once the training data has been collected and the model has been initiated, simulation times are reduced from hours to mere seconds while maintaining remarkable accuracy. Despite this promise, we also try to lay bare the current challenges of applying machine learning to these and more complex colloidal systems. [ABSTRACT FROM AUTHOR]

Location and characterization of a buried target from its electromagnetic induction response is a key problem for unexploded ordnance (UXO) detection. This article focuses on the influence of target size, depth, and orientation on its location and characterization on the basis of single dipole model with differential evolution (DE) algorithm against data collected by a portable transient electromagnetic (TEM) system. The sensor of the portable TEM system is composed of a single-layer transmitting coil and five three-component receiving coils. The diameter and current of transmitting coil are 0.5 m and 5 A. The length and resonant frequency of receiving coil are 5.6 cm and 180 kHz. The results of test-stand experiment show that the errors in location and characterization an underground target depend not only on the signal-to-noise ratio of the response, but also on the orientation of the target. For large target vertically (tail down) oriented, the estimated depth and characteristic response only represent the part of target close to the sensor, which are smaller than the real ones. For target flat-lying oriented, the algorithm overestimates both the depth and the characteristic response for the nonuniform primary field throughout the target. Finally, field experiment has been conducted. In general, the target can be located and characterized well even if the response of two targets is superimposed. The errors in estimated positions of about 5–7 cm support the conclusions from our test-stand experiment. These errors are especially critical when excavating targets.

This article presents a new analytical model for a permanent magnet that is particularly useful for calculating the magnetic force between two permanent magnets in a magnetic spring. The new model treats a single magnet as a pair of parallel magnetically charged surfaces, which we call dual-charged surfaces (DCSs). With the model, the force between two magnets is treated as the interaction of four charged surfaces, which can be calculated analytically as a function of magnets’ geometry and magnetization. This new model overcomes a major problem of other commonly used analytical models (dipole and point charge models) that predict infinitely large repulsive force when the separation distance between two magnets approaches zero and allows accurate calculation of the repulsive force in both near and far fields. The model is verified with experiments and finite element method (FEM) simulations through demonstrating correct prediction on the magnetic force versus separation over a wide range of the separation distance. With the root-mean-square deviation (RMSD) as a measure of the model accuracy, the DCS model is shown to have better accuracy over the Gilbert model (based on a pair of point charges), the Ampere model (based on a pair of dipoles), and the fitted polynomial method. [ABSTRACT FROM AUTHOR]

Using the charmonium light-front wavefunctions obtained by diagonalizing an effective Hamiltonian with the one-gluon exchange interaction and a confining potential inspired by light-front holography in the basis light-front quantization formalism, we compute production of charmonium states in diffractive deep inelastic scattering and ultra-peripheral heavy ion collisions within the dipole picture. Our method allows us to predict yields of all vector charmonium states below the open flavor thresholds in high-energy deep inelastic scattering, proton–nucleus and ultra-peripheral heavy ion collisions, without introducing any new parameters in the light-front wavefunctions. The obtained charmonium cross section is in reasonable agreement with experimental data at HERA, RHIC and LHC. We observe that the cross-section ratio σΨ(2s)/σJ/Ψ reveals significant independence of model parameters.

In this paper, hysteresis of magnetorheological (MR) fluids is identified from experimental tests following the mechanism of rate-independence and further studied to explore the hysteresis mechanism. The theoretical analysis based on the dipole model is provided to reveal the hysteresis mechanism of MR fluids. Specifically, the performance tests of a self-developed double-rod MR damper under different excitations show that instead of the typical force-velocity plot, the relationship between the force and displacement meets the requirements of rate-independence of the hysteresis well. A critical concept of “yield displacement” is defined and analyzed in the force-displacement plot to illustrate the hysteresis characteristics. In addition, the relationship of the normalized restoring force vs. strain is derived for a single chain from the dipole model. Then a stress-strain curve is developed for the multi-chain structure with an assumption of the dynamic equilibrium between the rupture and reconstruction of the chains. Sequentially, the hysteresis mechanism is established based on the force-displacement characteristics under reciprocating excitations. The consistency between the yield displacement in experiment and yield strain in theory verifies the effectiveness of the hypothetical hysteresis mechanism. The analysis results provide a guideline for the structural design of MR devices to enhance/reduce the hysteresis effect. The hysteresis mechanism-based further extension for the stress-strain properties of MR elastomers and the response time of MR fluids are provided as well.

One of the most common methods for performing non-destructive testing in steel tank floors is DC magnetic flux leakage (MFL). The magnetic dipole method is the most widely used mathematical technique to predict the MFL from defects in such structures. However, due to the complexity of an exact analytical description of an MFL system, researchers often make coarse approximations for the profile of the magnetic surface charge density $\sigma _{m}$ , orientation of the magnetic field H, and variation of relative permeability $\mu _{r}$. In this paper, the validity of these approximations is evaluated for 2-D rectangular defects in a steel plate, by comparing model predications with finite element results. The primary sources of deviation between the approximate solutions and true MFL profiles were found to be caused by assumptions that 1) $\sigma _{m}$ on the specimen surface adjacent to a flaw is zero. This assumption is equivalent to treating the orientation of H to be parallel to the specimen surface, even at locations in close proximity to a flaw and 2) local variation in permeability around the defect can be ignored. This approximation was found to cause an underestimation of $\sigma _{m}$ and, consequently, the predicted MFL. In contrast, approximating $\sigma _{m}$ to be zero at the bottom of a flaw, and approximating uniform distribution for $\sigma _{\mathbf {m}}$ on the vertical defect sides of a slot defect was found to generate only minor errors in an estimate of flux leakage. [ABSTRACT FROM AUTHOR]

Purpose. The application in electrostatic analogy of magnetostatics for inhomogeneous magnetized media of two known magnetization models. Methodology. A comparison of basic equations and formulas of electrostatic and magnetostatic field in immoveable isotropic inhomogeneous polarized medium for dipole model and the magnetization model by molecular currents is made. The value-analogues for dipole model of magnetization are established. Results. We have shown that the using of dipole model of magnetization is correct. There is not even formal analogy with electrostatic field in the case of using the magnetization model by molecular currents. The relation between the magnetizations for various models is obtained. It allows us to justify the using magnetization by molecular currents in electrostatic analogy. Originality. The magnetization for dipole model is introduced and the possibility of using magnetization by molecular currents in the formulas for calculating potential magnetostatic field in magnetized medium is substantiated. Practical value. The results allow to obtain correct formulation and solution of the problem of magnetostatic field calculation in inhomogeneous magnetized medium.

Four geomagnetic field models are discussed: IGRF, inclined, direct and simplified dipoles. Geomagnetic induction vector expressions are provided in different reference frames. Induction vector behavior is compared for different models. Models applicability for the analysis of satellite motion is studied from theoretical and engineering perspectives. Relevant satellite dynamics analysis cases using analytical and numerical techniques are provided. These cases demonstrate the benefit of a certain model for a specific dynamics study. Recommendations for models usage are summarized in the end. [ABSTRACT FROM AUTHOR]

The accuracy of a method for noninvasive localization of the origin of premature ventricular complex (PVC) was tested on simulated data. The method is based on inverse solution in terms of a single dipole that uses integrals of body surface potentials (BSPs) and a model of the torso volume conductor. ECGSIM software was used to simulate ectopic activation in a realistic ventricular model and BSPs on an inhomogeneous torso. Ectopic activation origins were simulated in 120 positions located in anterior, lateral, posterior, and septal segments of the right and left ventricle (RV, LV). In both septal segments 15 endocardial positions were specified, in all other segments 5 epicardial, 5 endocardial, and 5 in the valvular region were defined. Corresponding BSPs for initial 5 ms interval of the ectopic activity were simulated in 300 torso nodes as well as in 192 points representing BSP mapping leads. Simulated BSPs and the torso model with lungs and heart cavities were then used for the inverse localization of each PVC origin. The localization error (LE) was defined as the distance between the simulated and inversely estimated PVC origin position. All simulated PVC origins were localized in the correct ventricular segment. There was no significant difference between the LEs in the RV and LV, except the septal segments where the LE was significantly smaller in the RV (p<0.05). There were no significant differences between the LEs obtained using BSP maps from 300 torso nodes or 192 mapping leads (mean values LE300=5.2±4.4 mm and LE192=5.3±4.5 mm). [ABSTRACT FROM AUTHOR]

Using the charmonium light-front wavefunctions obtained by diagonalizing an effective Hamiltonian with the one-gluon exchange interaction and a confining potential inspired by light-front holography in the basis light-front quantization formalism, we compute production of charmonium states in diffractive deep inelastic scattering and ultra-peripheral heavy ion collisions within the dipole picture. Our method allows us to predict yields of all vector charmonium states below the open flavor thresholds in high-energy deep inelastic scattering, proton–nucleus and ultra-peripheral heavy ion collisions, without introducing any new parameters in the light-front wavefunctions. The obtained charmonium cross section is in reasonable agreement with experimental data at HERA, RHIC and LHC. We observe that the cross-section ratio σ Ψ ( 2 s ) / σ J / Ψ reveals significant independence of model parameters. [ABSTRACT FROM AUTHOR]

Modern fighter aircrafts, ships, missiles etc need to be very low Radar Cross Section (RCS) designs, to avoid detection by hostile radars. Hence accurate prediction of RCS of complex objects like aircrafts is essential to meet this requirement. A simple and efficient numerical procedure for treating problems of wide band RCS prediction Perfect Electric Conductor (PEC) objects is developed using Method of Moment (MoM). Implementation of MoM for prediction of RCS involves solving Electric Field Integral Equation (EFIE) for electric current using the vector and scalar potential solutions, which satisfy the boundary condition that the tangential electric field at the boundary of the PEC body is zero. For numerical purposes, the objects are modeled using planar triangular surfaces patches. Set of special sub-domain type basis functions are defined on pairs of adjacent triangular patches. These basis functions yield a current representation free of line or point charges at sub-domain boundaries. Once the current distribution is obtained, dipole model is used to find Scattering field in free space. RCS can be calculated from the scattered and incident fields. Numerical results for a square plate, a cube, and a sphere are presented over a bandwidth.

Simultaneous measurements of EEG-functional magnetic resonance imaging (fMRI) combine the high temporal resolution of EEG with the distinctive spatial resolution of fMRI. The purpose of this EEG-fMRI study was to search for hemodynamic responses (blood oxygen level-dependent - BOLD responses) associated with interictal activity in a case of right mesial temporal lobe epilepsy before and after a successful selective amygdalohippocampectomy. Therefore, the study found the epileptogenic source by this noninvasive imaging technique and compared the results after removing the atrophied hippocampus. Additionally, the present study investigated the effectiveness of two different ways of localizing epileptiform spike sources, i.e., BOLD contrast and independent component analysis dipole model, by comparing their respective outcomes to the resected epileptogenic region. Our findings suggested a right hippocampus induction of the large interictal activity in the left hemisphere. Although almost a quarter of the dipoles were found near the right hippocampus region, dipole modeling resulted in a widespread distribution, making EEG analysis too weak to precisely determine by itself the source localization even by a sophisticated method of analysis such as independent component analysis. On the other hand, the combined EEG-fMRI technique made it possible to highlight the epileptogenic foci quite efficiently.

In this paper, we present an improved analytical 3-D magnetic flux leakage (MFL) model of the field due to the occurrence of a surface-breaking defect in a ferromagnetic specimen. This model is based on our recent magnetic dipole model (MDM) of the MFL field, which was derived from the first principles of Maxwell’s equations. The MDM assumes a ferromagnetic specimen with a small defect exposed to a uniform external magnetic field, which is strong enough to saturate the specimen locally and causes uniform magnetization around the defect. Under this assumption, the MFL field can be mathematically described as if it is caused by magnetic charges on the surface of the defect. The magnitude and the sign of these magnetic charges are given by the magnetization vector and the local unit vector normal to the surface of the defect. Our original MDM uses only one parameter to describe the normal vector, and can only be used to analyze simple defect shapes, such as cylinders and cuboids. Our improved model in this paper uses two parameters to describe the normal vector, and can be used to analyze a wider range of defects, such as cones, ellipsoids, and real defect shapes. We illustrate our improved model by comparing its solution to that of the original MDM and validating it with the finite-element method simulations for different defect shapes. Our analysis shows that the improved model gives a good approximation of the MFL fields for a much wider range of defect shapes than the original MDM does. [ABSTRACT FROM PUBLISHER]

Despite evoked potentials' (EP) ubiquity in research and clinical medicine, insights are limited to gross brain dynamics as it remains challenging to map surface potentials to their sources in specific cortical regions. Multiple sources cancellation due to cortical folding and cross-talk obscures close sources, e.g. between visual areas V1 and V2. Recently retinotopic functional magnetic resonance imaging (fMRI) responses were used to constrain source locations to assist separating close sources and to determine cortical current generators. However, an fMRI is largely infeasible for routine EP investigation. We developed a novel method that replaces the fMRI derived retinotopic layout (RL) by an approach where the retinotopy and current estimates are generated from EEG or MEG signals and a standard clinical T1-weighted anatomical MRI. Using the EEG-RL, sources were localized to within 2 mm of the fMRI-RL constrained localized sources. The EEG-RL also produced V1 and V2 current waveforms that closely matched the fMRI-RL's ( n = 2) r(1,198) = 0.99, P < 0.0001. Applying the method to subjects without fMRI ( n = 4) demonstrates it generates waveforms that agree closely with the literature. Our advance allows investigators with their current EEG or MEG systems to create a library of brain models tuned to individual subjects' cortical folding in retinotopic maps, and should be applicable to auditory and somatosensory maps. The novel method developed expands EP's ability to study specific brain areas, revitalizing this well-worn technique. Hum Brain Mapp 37:1696-1709, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This paper presents the application of a bio-inspired method for optimizing a lifelike vectorcardiographic (VCG) model. During the model estimation, a Particle Swarm Optimization (PSO) seeks the optimal combination of all parameters that maximize the correlation coefficient ( r ) and minimize the Mean Squared Error (MSE) between the synthetic and directly measured VCG leads. The proposed method was tested on 52 different VCG records annotated as a healthy control (HC) from PTB database. 156 models were individualized without any previous analysis of the waves of the original records. The PSO method automatically provides very realistic models with a correlation coefficient r > 0.995 and MSE < 0.0005 mV 2 for 152 of the 156 VCG signals. [ABSTRACT FROM AUTHOR]

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Cortical stimulation via electrocorticography (ECoG) may be an effective method for inducing artificial sensation in bi-directional brain-computer interfaces (BD-BCIs). However, strong electrical artifacts caused by electrostimulation may significantly degrade or obscure neural information. A detailed understanding of stimulation artifact propagation through relevant tissues may improve existing artifact suppression techniques or inspire the development of novel artifact mitigation strategies. Our work thus seeks to comprehensively characterize and model the propagation of artifacts in subdural ECoG stimulation. To this end, we collected and analyzed data from eloquent cortex mapping procedures of four subjects with epilepsy who were implanted with subdural ECoG electrodes. From this data, we observed that artifacts exhibited phase-locking and ratcheting characteristics in the time domain across all subjects. In the frequency domain, stimulation caused broadband power increases, as well as power bursts at the fundamental stimulation frequency and its super-harmonics. The spatial distribution of artifacts followed the potential distribution of an electric dipole with a median goodness-of-fit of R 2 = 0.80 across all subjects and stimulation channels. Artifacts as large as ±1,100 μV appeared anywhere from 4.43 to 38.34 mm from the stimulation channel. These temporal, spectral and spatial characteristics can be utilized to improve existing artifact suppression techniques, inspire new strategies for artifact mitigation, and aid in the development of novel cortical stimulation protocols. Taken together, these findings deepen our understanding of cortical electrostimulation and provide critical design specifications for future BD-BCI systems., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Lim, Wang, Shaw, Gong, Armacost, Liu, Do, Heydari and Nenadic.)

Two modified versions of the dipole model with a pair of mediating fields are considered. In the first version, the modification affects the Yukawa term in the Lagrangian. In the second version a non-linear self-action term is added. By constructing exact solutions of the field equations with the use of a covariant Green function we derive a Lagrangian with many-point time-nonlocal interaction terms. For the linear dipole model the two-particle interaction, in the non-relativistic limit, is shown to be a sum of Coulomb and linear confinement terms. For the nonlinear φ3-model the interactions are shown to include pairwise potentials and also three-particle cluster potentials with a logarithmic confinement. The approaches towards a consistent relativistic treatment of the models are proposed, and the problem of divergences is discussed. [ABSTRACT FROM AUTHOR]